Songklanakarin Journal of Science and Technology (SJST) (May 2005)
Effects of extracts from Tiam seeds on cotton leafworm
Abstract
Crude n-hexane and methanolic extracts from the seeds of Azadirachta excelsa Jack. (Tiam) and A. indica var. siamensis Valeton (Neem), Bacillus thuringiensis var. kurstaki HD-1 and permethrin were tested for mortality effect on the 2nd, 3rd and the 4th instar larvae of cotton leafworm (Spodoptera litura F.) by topical application and spraying methods. Among the seed extracts, crude methanolic extract from A. excelsa was the most effective. Its LC50, by topical application, at 72 hours after tested on the 2nd, 3rd and the 4th instar larvae was 5.26, 8.83 and 19.69 g/l, respectively, and by feeding was 1.59, 3.67 and 4.72 g/l, respectively. Crude methanolic extract was more effective than the crude n-hexane extract in each particular plant. Among tested samples, permethrin, a semi-synthetic chemical insecticide, showed the highest insecticidal effect. Its LC50, by topical application, at 72 hours after tested on the 2nd, 3rd and the 4th instar larvae was 0.12, 0.18 and 1.44 g/l, respectively, and by feeding was 0.08, 0.11 and 0.34 g/l, respectively. Use of the crude methanolic extract of A. excelsa to reduce the population of the 2nd instar larvae of cotton leafworm on Chinese kale (Brassica alboglabra Bailey) was more effective than that of crude methanolic extract of A. indica var. siamensis.
